A track vehicle (crawler dozer, crawler loader, track excavator, etc.) has an undercarriage with one or more track units on either side of the vehicle. Each track unit has an endless track trained about a drive sprocket (e.g., at the rear), one or more idlers (e.g., one at the front), and one or more lower track rollers in contact with the low pass of the endless track extending between the front and rear of the endless track. Each roller may be mounted to and positioned under a track frame (e.g., to which the sprocket may be rotatably coupled) or a recoil frame (to which an idler may be rotatably coupled) coupled to the track frame and recoilable relative thereto in response to, for example, ground impact forces.
In larger track vehicles, track roller bogies have been used. An exemplary a track roller bogie includes a mounting arm, a pivot arm, and two lower track rollers. The mounting arm is coupled pivotally to a frame (in some cases the track frame and in other cases the recoil frame) by use of a first pivot joint allowing pivotal movement of the mounting arm relative to that frame about an axis of the first pivot joint. The roller pivot arm is coupled pivotally to the mounting arm at a second pivot joint positioned between the two rollers allowing pivotal movement of the roller pivot arm and the two rollers coupled thereto relative to the mounting arm about an axis of the second pivot joint. Such a configuration of the track roller bogie enhances the ability of the endless track to marry the contours of the ground, promoting tractive effort and thus the operational capability of the track vehicle (e.g., the dozing capability of a crawler dozer).